1. Field of the Invention
The present invention relates to a label for use in in-mold forming in which the label is set beforehand in a mold so that the printed side of the label comes into contact with the mold wall surface and a labeled container is produced by introducing a parison of a molten thermoplastic resin into the mold to conduct blow molding, by injection-molding a molten thermoplastic resin in the mold, or by subjecting a sheet of a molten thermoplastic resin to vacuum forming or pressure forming with the mold. The invention further relates to a resin container bearing the label, a process for producing the label, and a process for producing the labeled resin container.
2. Description of the Related Art
For integrally molding a labeled resin container, a process has been used which comprises inserting a blank or label into a mold beforehand and then molding a container in the mold by injection molding, blow molding, pressure-difference molding, foam molding, or the like to label the container for decoration, etc. (see JP-A-58-69015 and EP-A-254, 923). Known labels for use in such in-mold forming include resin films printed by gravure printing, synthetic papers printed by multicolor offset printing (see, for example, JP-B-2-7814 and JP-A-2-84319), and aluminum labels obtained by laminating a high-pressure-process low-density polyethylene, linear low-density polyethylene, ethylene/vinyl acetate copolymer, or ethylene/acrylic acid copolymer to the back side of an aluminum foil and printing the front side of the foil by gravure printing. Also known is a label which comprises a heat-sealable polyethylene resin layer having an antistatic layer on a surface thereof and having a specific value of wettability index and which is thus inhibited from arousing troubles attributable to electrostatic buildup in a label printing step and an in-mold forming step in a low-humidity environment, e.g., in winter (Japanese patent application No. 2004-151318).
However, the rate of container molding by the in-mold forming is being increased for the purpose of improving the productivity of the in-mold forming. Namely, the cooling time for cooling the resin container in the mold is being reduced and the temperature to which the mold is cooled is being lowered. In the case where the material of the container is a polyethylene resin, adhesion between the label and the container is relatively satisfactory. However, when the material of the container is a polypropylene resin, which is more transparent than polyethylene resins, then adhesion between the label and the container tends to be considerably low because of the low temperature to which the mold is cooled. This labeled container has drawbacks that the label readily peels off the container and has many blisters. There has hence been a problem that a high container loss results. The market for transparent containers comprising a polypropylene resin is growing because the amount and state of the contents thereof can be ascertained.
In the case where a polymer having a low melting point, such as, e.g., an ethylene/vinyl acetate copolymer or an ethylene/acrylic acid copolymer, is used as a heat-sealable resin in the label, relatively satisfactory adhesion to polypropylene containers is obtained. However, it has been pointed out that this label has a problem concerning suitability for filling with hot contents, i.e., the label readily peels off or slides when the temperature of the contents of the container is about 90° C.